U.S. patent number 10,775,803 [Application Number 16/064,866] was granted by the patent office on 2020-09-15 for docking system and method for charging a mobile robot.
This patent grant is currently assigned to POLITECNICO DI TORINO, TELECOM ITALIA S.p.A.. The grantee listed for this patent is POLITECNICO DI TORINO, TELECOM ITALIA S.p.A.. Invention is credited to Gian Piero Fici, Marco Gaspardone, Miguel Efrain Kaouk Ng, Matteo Lazzarin.
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United States Patent |
10,775,803 |
Fici , et al. |
September 15, 2020 |
Docking system and method for charging a mobile robot
Abstract
A docking system and method for charging a mobile robot at a
docking station. The system includes a first module for the robot,
including a first communication unit and a first control unit, and
a second module for the station, including a second communication
unit, one or more docking sensors, and a second control unit. When
the robot enters a docking region around the station, the first
communication unit sends to the second communication unit a status
message indicating that the robot needs charging; upon reception of
the status message, the second control unit uses the sensors to
derive a traction command to drive the robot towards the station;
and the second communication unit sends to the first communication
unit a command message containing the traction command. The first
control unit processes the traction command and uses it to operate
traction motors of the robot.
Inventors: |
Fici; Gian Piero (Turin,
IT), Gaspardone; Marco (Turin, IT), Kaouk
Ng; Miguel Efrain (Turin, IT), Lazzarin; Matteo
(Turin, IT) |
Applicant: |
Name |
City |
State |
Country |
Type |
TELECOM ITALIA S.p.A.
POLITECNICO DI TORINO |
Milan
Turin |
N/A
N/A |
IT
IT |
|
|
Assignee: |
TELECOM ITALIA S.p.A. (Milan,
IT)
POLITECNICO DI TORINO (Turin, IT)
|
Family
ID: |
55066641 |
Appl.
No.: |
16/064,866 |
Filed: |
December 30, 2015 |
PCT
Filed: |
December 30, 2015 |
PCT No.: |
PCT/EP2015/081406 |
371(c)(1),(2),(4) Date: |
June 21, 2018 |
PCT
Pub. No.: |
WO2017/114571 |
PCT
Pub. Date: |
July 06, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180373258 A1 |
Dec 27, 2018 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G05D
1/0282 (20130101); G05D 1/0231 (20130101); G05D
1/0225 (20130101); G05D 1/0276 (20130101); H02J
7/0047 (20130101); H02J 7/00045 (20200101); H02J
7/00034 (20200101) |
Current International
Class: |
G05D
1/02 (20200101); H02J 7/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
2 935 640 |
|
Jul 2015 |
|
CA |
|
1 746 477 |
|
Jan 2007 |
|
EP |
|
2 617 531 |
|
Jul 2013 |
|
EP |
|
2 865 622 |
|
Apr 2015 |
|
EP |
|
WO 2014/114910 |
|
Jul 2014 |
|
WO |
|
Other References
International Search Report dated Sep. 2, 2016 in PCT/EP2015/081406
filed Dec. 30, 2015. cited by applicant.
|
Primary Examiner: Rink; Ryan
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Nuestadt, L.L.P.
Claims
The invention claimed is:
1. A docking system for charging a mobile robot at a docking
station, the system comprising: a first module configured to be
installed on board the mobile robot; and a second module configured
to be installed on board the docking station; the first module
comprising a first communication unit and a first control unit, the
second module comprising a second communication unit, one or more
docking sensors and a second control unit; wherein: when the mobile
robot enters a docking region around the docking station, the first
communication unit is configured to send to the second
communication unit a status message indicating that the mobile
robot needs charging; the second control unit is configured to,
upon reception of the status message, use the one or more docking
sensors, the one or more sensors detecting a position of the mobile
robot away from the docking station, to derive, based on data
received by the one or more docking sensors, a traction command to
drive the mobile robot towards the docking station; and the second
communication unit is configured to send to the first communication
unit a command message containing the traction command; and wherein
the first control unit is configured to process the traction
command and use the traction command to operate one or more
traction motors of the mobile robot.
2. The docking system according to claim 1, wherein the second
communication unit is configured to, upon reception of the status
message, send to the first communication unit an acknowledgment
message.
3. The docking system according to claim 2, wherein the second
control unit is further configured to command switching off
components of the mobile robot, while keeping switched on at least
the first module, the one or more traction motors, and circuitries
driving them.
4. The docking system according to claim 1, wherein the second
control unit is configured to, upon reception of the status
message, switch on the one or more docking sensors.
5. The docking system according to claim 1, wherein the data
received by the one or more docking sensors comprise a distance and
an orientation between the mobile robot and the docking station,
and wherein the command message comprises a translational speed
and/or a rotational speed to be actuated by the one or more
traction motors of the mobile robot, the translational speed being
computed based on the distance and the rotational speed being
computed based on the orientation.
6. The docking system according to claim 1, wherein the status
message and the command message are messages according to Robot
Operating System (ROS) rules.
7. The docking system according to claim 1, wherein, until the
mobile robot docks on the docking station: the second control unit
is further configured to cyclically derive, based on further data
received by the one or more docking sensors, a further traction
command; the second communication unit is further configured to
cyclically send to the first communication unit a further command
message containing the further traction command; and the first
control unit is further configured to cyclically process the
further traction command and use the traction command to operate
the one or more traction motors of the mobile robot.
8. The docking system according to claim 7, wherein the first
module comprises a first power handling unit with first electrical
contacts configured to establish an electrical connection with
second electrical contacts of a second power handling unit of the
second module when the mobile robot docks on the docking
station.
9. The system according to claim 1, wherein the first communication
unit and the second communication unit are configured to establish
a connection according to a wireless communication technology, the
wireless communication technology being one of WiFi, 4G LTE.
10. The system according to claim 1, wherein the first
communication unit and the second communication unit are configured
to establish a connection through a cloud computing platform.
11. A method for charging a mobile robot at a docking station, the
method comprising: a) when the mobile robot enters a docking region
around the docking station, sending by the mobile robot to the
docking station a status message indicating that the mobile robot
needs charging; b) at the docking station, upon reception of the
message, using one or more docking sensors, the one or more sensors
detecting a position of the mobile robot away from the docking
station, to derive, based on data received by the one or more
docking sensors, a traction command to drive the mobile robot
towards the docking station; c) at the docking station, sending to
the mobile robot a command message containing the traction command;
and d) at the mobile robot, processing the traction command and
using it to operate one or more traction motors of the mobile
robot.
12. The method according to claim 11, further comprising, at the
docking station, upon reception of the status message, sending to
the mobile robot an acknowledgment message, and, at the mobile
robot, upon reception of the acknowledgment message, switching off
components of the mobile robot, while keeping switched on at least
the first module, the one or more traction motors and circuitries
driving them.
13. The method according to claim 11, wherein b) to d) are
cyclically repeated until the mobile robot docks on the docking
station.
14. The method according to claim 13, wherein b) to d) are
cyclically repeated until first electrical contacts of the mobile
robot establish an electrical connection with second electrical
contacts of the docking station.
15. The method according to claim 11, wherein the docking region is
a circular region around the docking station of radius between 1
meter and 10 meters.
Description
TECHNICAL FIELD
The present invention relates to the field of mobile robots. In
particular, the present invention relates to a docking system and
method for charging a mobile robot.
BACKGROUND ART
Mobile robots are nowadays becoming popular for performing simple
and repetitive tasks, such as household maintenance (floor
cleaning), or dangerous tasks, for instance inspection or
surveillance activities inside environments where humans are at
risk.
Typically, mobile robots may be controlled remotely by a human
operator or they may operate autonomously. This latter type of
operation implies that the mobile robot is capable of autonomous
indoor navigation, which means that the robot is capable of
creating a map of the indoor environment, determining its
localization within the map and planning a path to navigate
point-to-point within the map.
Generally, an autonomous mobile robot may be provided with electric
traction motors. In this case, it is also provided with an on-board
power unit (i.e. a battery) that is periodically recharged.
Recharging is performed at a docking station connected to the
electric power distribution network. When the on-board battery is
to be recharged, the autonomous mobile robot typically moves
towards the docking station. In the vicinity of the docking
station, the mobile robot starts a docking operation according to
which the mobile robot determines the exact position of the docking
station and generates motion commands for its traction motors, in
order to approach the docking station and connect to it. Typically,
the position of the docking station may be determined by the mobile
robot by detecting, through appropriate sensors, signals emitted by
the docking station, which may comprise infrared beacons and light
signals, or by recognizing reference images or visual markers
located on the docking station, or by detecting an audio marker
emitted by the docking station or by a sound source in the vicinity
of the docking station.
WO2014/114910 discloses a docking station for a mobile robot
comprising a base portion that is locatable on a floor surface and
a rear portion that is pivotable with respect to the base portion,
thereby permitting a user to place the docking station on the floor
in an unfolded configuration but to store the docking station in a
folded configuration.
EP2617531A1 discloses an intelligent robot system comprising an
intelligent robot and a charging base. The intelligent robot
comprises a docking electrode, a walking mechanism and a control
unit. The docking electrode, the walking mechanism and the control
unit are disposed in the body of the intelligent robot. The
charging base comprises a charging electrode disposed on the body
of the charging base. The intelligent robot further comprises a
gripping mechanism. When the docking electrode and the charging
electrode dock successfully, the control unit controls the gripping
mechanism to lock the walking mechanism to enable the intelligent
robot to maintain a successful docking state in the charging base,
preventing the charging electrode of the charging base from being
separated from the docking electrode due to the improper movement
of the walking mechanism. Any interference during of the
intelligent robot is thus prevented and charging efficiency is
improved.
U.S. Pat. No. 7,546,179 discloses a method and apparatus allowing a
mobile robot to return to a designated location the method
including: calculating a first direction angle of the mobile robot
at a second location arrived at after the mobile robot travels a
predetermined distance from the first location; determining whether
the mobile robot approaches or moves away from the designated
location, at a third location arrived at after the mobile robot
rotates by the first direction angle and then travels a
predetermined distance; and if the result of the determination
indicates that the mobile robot approaches the docking station,
controlling the mobile robot to travel according to the first
direction angle, and if the result indicates the mobile robot moves
away from the docking station, calculating a second direction angle
of the mobile robot at the third location, and controlling the
mobile robot to travel according to the second direction angle.
U.S. Pat. No. 7,332,890 discloses a method for energy management in
a robotic device includes providing a base station for mating with
the robotic device, determining a quantity of energy stored in an
energy storage unit of the robotic device, and performing a
predetermined task based at least in part on the quantity of energy
stored. Also disclosed are systems for emitting avoidance signals
to prevent inadvertent contact between the robot and the base
station, and systems for emitting homing signals to allow the
robotic device to accurately dock with the base station.
SUMMARY OF THE INVENTION
The Applicant has noticed that known systems and methods for
charging a mobile robot have some drawbacks.
In particular, the Applicant has noticed that the mobile robot
often does not correctly dock on the docking station at its first
attempt. This may be due to the fact that when the mobile robot is
docking on the docking station, its movements may be imprecise
because of a number of factors. These factors may include:
inaccuracies in the docking station geometry model, which affect
the autonomous navigation algorithms; lack of reference signals and
markers at a reduced distance between the mobile robot and the
docking station; fluctuations of the intensity of the reference
signals and markers during the docking operation; and low battery
level of the on-board power unit.
These factors may negatively impact on the docking operation as the
robot may be forced to repeat the operation of localizing the
docking station and the manoeuvres for approaching it and
connecting to it. Repeating the docking operation disadvantageously
may reduce the charging level of the on board battery of the mobile
robot to a value that does not allow the mobile robot to complete
the procedure and dock on the docking station. The mobile robot may
even go dead before docking on the docking station, which implies
that a human operator shall reach the mobile robot and carry it to
the docking station for recharging. This is clearly inefficient and
time consuming.
Moreover, typically, in order to carry out the docking operation
the mobile robot should switch on one or more sensors and keep them
switched on until the procedure gets completed. Sensors may
comprise a laser scanner, an infrared sensor, a videocamera, an
ultrasonic sensor. This implies that the mobile robot is consuming
a large amount of energy during the docking operation and that the
on board battery of the mobile robot may discharge quickly, hence
reducing the time interval that is available for completing the
docking operation.
In view of the above, the Applicant has tackled the problem of
providing a docking system and method for charging a mobile robot
which allows minimizing the energy consumption of the robot during
the docking operations. Minimizing the energy consumption would
allow the mobile robot to complete the docking operation even in
presence of one or more of the factors listed above (inaccuracies
in the docking station geometry model, lack or fluctuations of
reference signals at reduced distances, low battery level).
According to a first aspect, the present invention provides a
docking system for charging a mobile robot at a docking station,
the system comprising a first module configured to be installed on
board the mobile robot, and a second module configured to be
installed on board the docking station, the first module comprising
a first communication unit and a first control unit, the second
module comprising a second communication unit, one or more docking
sensors and a second control unit, wherein: when the mobile robot
enters a docking region around the docking station, the first
communication unit is configured to send to the second
communication unit a status message indicating that the mobile
robot needs charging; the second control unit is configured to,
upon reception of the status message, use the one or more docking
sensors to derive, on the basis of data received by the one or more
docking sensors, a traction command to drive the mobile robot
towards the docking station; and the second communication unit is
configured to send to the first communication unit a command
message containing the traction command, and wherein the first
control unit is configured to process the traction command and use
it to operate one or more traction motors of the mobile robot.
Preferably, the second communication unit is configured to, upon
reception of the status message, send to the first communication
unit an acknowledgment message.
Preferably, the second control unit is further configured to
command switching off a number of components of the mobile robot,
while keeping switched on at least the first module, the one or
more traction motors and circuitries driving them.
According to an embodiment of the present invention, the second
control unit is configured to, upon reception of the status
message, switch on the one or more docking sensors.
Preferably, the data received by the one or more docking sensors
comprise a distance and an orientation between the mobile robot and
the docking station, wherein the command message comprises a
translational speed and/or a rotational speed to be actuated by the
one or more traction motors of the mobile robot, the translational
speed being computed on the basis of the distance and the
rotational speed being computed on the basis of the
orientation.
Preferably, the status message and the command message are messages
according to a robot operating system.
According to embodiments of the present invention: the second
control unit is further configured to cyclically derive, on the
basis of further data received by the one or more docking sensors,
a further traction command; the second communication unit is
further configured to cyclically send to the first communication
unit a further command message containing the further traction
command; and the first control unit is further configured to
cyclically process the further traction command and use it to
operate the one or more traction motors of the mobile robot, until
the mobile robot docks on the docking station.
Preferably, the first module comprises a first power handling unit
with first electrical contacts configured to establish an
electrical connection with second electrical contacts of a second
power handling unit of the second module when the mobile robot
docks on the docking station.
Preferably, the first communication unit and the second
communication unit are configured to establish a connection
according to a wireless communication technology, the wireless
communication technology being one of Bluetooth.RTM., WiFi, 4G LTE.
Alternatively or in addition, the first communication unit and the
second communication unit are configured to establish a connection
through a cloud computing platform.
According to a second aspect, the present invention provides a
method for charging a mobile robot at a docking station, the method
comprising: a) when the mobile robot enters a docking region around
the docking station, sending by the mobile robot to the docking
station a status message indicating that the mobile robot needs
charging; b) at the docking station, upon reception of the message,
using one or more docking sensors to derive, on the basis of data
received by the one or more docking sensors, a traction command to
drive the mobile robot towards the docking station; c) at the
docking station, sending to the mobile robot a command message
containing the traction command; and d) at the mobile robot,
processing the traction command and using it to operate one or more
traction motors of the mobile robot Preferably, the method further
comprises, at the docking station, upon reception of the status
message, sending to the mobile robot an acknowledgment message,
and, at the mobile robot, upon reception of the acknowledgment
message, switching off a number of components of the mobile robot,
while keeping switched on at least the first module, the one or
more traction motors and circuitries driving them.
Preferably, steps b to d are cyclically repeated until the mobile
robot docks on the docking station.
More preferably, steps b to d are cyclically repeated until first
electrical contacts of the mobile robot establish an electrical
connection with second electrical contacts of the docking
station.
Preferably, the docking region is a circular region around the
docking station of radius comprised between 1 m and 10 m.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become clearer from the following
detailed description, given by way of example and not of
limitation, to be read with reference to the accompanying drawings,
wherein:
FIG. 1 schematically shows a docking station and a mobile robot in
a reference Cartesian coordinate system;
FIG. 2 shows a block scheme of an exemplary docking system for
charging the mobile robot according to the present invention;
and
FIG. 3 is a flowchart of the docking method for charging a mobile
robot according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The present invention applies to a robotic system including a
mobile robot and a docking station. An exemplary robotic system 1
is represented in FIG. 1, comprising a mobile robot 11 and a
docking station 12. In FIG. 1, the system 1 is represented within
reference Cartesian coordinate axes X, Y whose origin coincides
with the location of the docking station. The mobile robot 11 is at
a distance D from the docking station 12, the distance D being
variable with time, and has an orientation .theta. with respect to
the docking station 12, the orientation .theta. being computed as
the angle, variable with time, between a reference coordinate axis,
for instance the Y axis, and the straight line joining the docking
station 12 and the mobile robot 11.
As generally known in the art, the mobile robot may comprise one or
more electric traction motors for operating traction members
allowing the robot to perform translational and rotational
movements. The traction members may include one or more pairs of
wheels, or a pair of tracks, or robotic legs (in humanoid robots).
The tractions members enable the mobile robot to move in a forward
and a reverse direction and to follow a curved path. The mobile
robot 11 is also provided with a rechargeable power source, such as
a 12V on-board battery, configured to supply power to the mobile
robot components, in particular to the traction motors. Further,
the mobile robot 11 may comprise a powerboard that is connected to
the rechargeable power source and provides the necessary power to
the mobile robot components. The mobile robot 11 may comprise other
components that are not described here as they are not relevant to
the present description.
The mobile robot 11 to which the present invention applies is
autonomous in that it includes an autonomous navigation unit that
enables it to autonomously navigate the environment in which it is
located. The autonomous navigation unit of the mobile robot 11
comprises a processor (or microprocessor) and one or more
navigation sensors. The navigation sensors provide navigation data
to the processor of the navigation unit for calculating the
position of the mobile robot 11 inside the considered environment
and determining the mobile robot route according to a known
autonomous navigation algorithm. Known algorithms for autonomous
navigation may comprise Adaptive Monte Carlo Localization (AMCL),
Rapidly Exploring Random Tree (RRT), Smooth Nearness Diagram (SND),
Vector Field Histogram (VFH). The one or more navigation sensors
may comprise a laser scanner. An exemplary laser scanner that may
be used is the UTM-30LX laser scanner by Hokuyo Automatic Co.,
LTD.
It should be noted that autonomous navigation algorithms and
navigation sensors are generally known in the art. As these
components do not form part of the present invention, a more
detailed description of the autonomous navigation algorithms and
navigation sensors will be omitted here.
Moreover, the docking station 12 is preferably attached to an
electrical power distribution network.
The mobile robot 11 and the docking station 12 are configured to be
associated one with the other so that the mobile robot 11 may
recharge its power source when the power level of the power source
is below a given threshold. In particular, the docking system and
method of the present invention provide for driving the mobile
robot 11 towards the docking station until it connects to it. For
the application of the docking method and the operation of the
docking system, it is assumed that the mobile robot 11 has
autonomously reached a "docking region" in the proximity of the
docking station. A "docking region" within the meaning of the
present invention is a circular area of radius R around the docking
station. Preferably, the radius R of the docking region is equal to
a value ranging from few meters (e.g. 1 m) to 10 meters.
FIG. 2 shows a block scheme of a docking system 2 for charging the
mobile robot according to an embodiment of the present invention.
The system 2 preferably comprises a first module 21 to be
associated with the mobile robot 11 and a second module 22 to be
associated with the docking station 12. In particular, the first
module 21 is preferably positioned on board the mobile robot 11.
The second module 22 is preferably positioned on board the docking
station 12.
The first module 21 preferably comprises a first communication unit
211, a first power handling unit 212 and a first control unit 213.
The first communication unit 211 is preferably connected to the
first control unit 213 which is in turn connected to the first
power handling unit 212. The first communication unit 211
preferably comprises a wireless interface configured to transmit
and receive wireless signals to/from a corresponding unit comprised
within the second module 22 of the docking station 12, as it will
be described in greater detail herein after.
The second module 22 preferably comprises a second communication
unit 221, a second power handling unit 222, a second control unit
223 and one or more docking sensors 224. The second communication
unit 221 is preferably connected to the second control unit 223,
which is in turn connected to the second power handling unit 222
and to the one or more docking sensors 224. The second
communication unit 221 preferably comprises a wireless interface
configured to transmit and receive wireless signals to/from the
first communication unit 211 comprised within the first module 21
of the mobile robot 11, as it will be described in greater detail
herein after.
The first communication unit 211 and the second communication unit
221 are preferably configured to exchange information and commands
in the form of messages carried by wireless signals over a wireless
bidirectional communication link which is established between them.
The communication link may be a direct communication link
established between the first communication unit 211 and the second
communication unit 221 through a wireless communication technology
such as Bluetooth.RTM. or WiFi. For instance, the first
communication unit 211 and the second communication unit 221 may
each connect to an external WiFi hotspot in order to establish a
connection. In case the Bluetooth.RTM. or WiFi technology is used,
the first communication unit 211 and the second communication unit
221 may each comprise a dedicated antenna. Alternatively or in
addition, the first communication unit 211 and the second
communication unit 221 may each comprise an 4G LTE (Long Term
Evolution) module which provides a 4G LTE connection. Further
alternatively or in addition, the first communication unit 211 and
the second communication unit 221 may be remotely connected to a
cloud computing platform 23 and they may establish a connection
through the cloud platform. In this case, each of the first
communication unit 211 and the second communication 221 comprises a
respective independent cloud agent, which is connected to the cloud
platform 23 though a wireless communication technology such as WiFi
or 4G LTE. The cloud platform 23 may be installed on a remote
server or it may be distributed on a number of servers.
The first power handling unit 212 preferably comprises an electric
circuit configured to receive a supply voltage for charging the
mobile robot 11 when the mobile robot 11 is connected to the
docking station 12. The first power handling module 212 further
comprises a mechanical structure which allows to physically connect
the mobile robot 11 to the docking station 12. Moreover, the first
power handling unit 212 comprises first electrical contacts that
provide an electrical connection with corresponding contacts on the
docking station 12 when the mobile robot 11 docks on the docking
station 12.
The second power handling unit 222 preferably comprises an electric
circuit configured to provide the supply voltage for charging the
mobile robot 11 when the mobile robot 11 is connected to the
docking station 12. The supply voltage is retrieved from the
electrical power distribution network. The second power handling
module 222 further comprises a mechanical structure which is
configured to engage with the corresponding mechanical structure of
the first power handling module 212 in order to physically connect
the mobile robot 11 to the docking station 12. Moreover, the second
power handling unit 222 comprises second electrical contacts that
provide an electrical connection with the corresponding contacts on
the mobile robot 11 when the mobile robot 11 docks on the docking
station 12.
According to an embodiment of the present invention, the first
power handling module 212 may comprise a flat surface mechanical
structure having a set of electrical contacts in the form of
couples of pins of a elongated shape, which protrude, at least
partially, from the external surface of the mobile robot 11.
Moreover, the second power handling module 222 may comprise a
mechanical structure having a convex surface with electrical
contacts in the form of metallic elongated bands. The contacting
bands should be positioned on the exterior of the docking station
12 so as to allow contacting the pins of the mobile robot 11 when
the mobile robot 11 docks on the docking station 12.
The electrical contacts described above advantageously allow
accommodating a range of lateral and angular misalignments between
the mobile robot 11 and the docking station 12 when the mobile
robot 11 docks on the docking station 12.
The first control unit 213 is preferably configured to process
traction commands received by the mobile robot 11 from the docking
station 12 through the first communication unit 211 and the second
communication unit 221, the traction commands comprising
information related to translational and/or rotational movements
that the mobile robot 11 should perform in order to approach the
docking station 12. The first control unit 213 is further
preferably configured to, on the basis of the traction commands,
generate corresponding control signals to operate the traction
motors of the mobile robot 11 so that the mobile robot 11 may
approach the docking station 12 and connect to it, as it will be
described in greater detail herein after. Furthermore, the first
control unit 213 is configured to communicate with the powerboard
of the mobile robot 11 for switching on and off the mobile robot
components.
The second control unit 223 is preferably configured to iteratively
compute a distance and an orientation between the docking station
12 and the mobile robot 11 while the mobile robot is approaching
the docking station 12, as it will be described in greater detail
herein after. Furthermore, the second control unit 223 is
configured to, on the basis of the distance and orientation of the
mobile robot 11 with respect to the docking station 12, generate
the traction commands that are required for driving the mobile
robot 11 towards the docking station 12 until it docks on the
docking station 12.
The computation of the distance and orientation of the mobile robot
11 with respect to the docking station 12 is preferably performed
by the second control unit 223 on the basis of data sensed by the
one or more docking sensors 224 installed on board the docking
station 12. Each sensor of the one or more sensors 224 installed on
board the docking station 12 is preferably configured to, when
switched on, emit a respective docking signal within the
surrounding environment allowing to compute the distance and
orientation of the mobile robot so that the docking station 12 may
drive the mobile robot 11 to reach the docking station 12 and
connect to it, as it will be described in greater detail herein
after. These one or more sensors 224 may comprise one or more of: a
light sensor, such as a laser scanner, an infrared proximity
sensor, such as a PIR (Passive InfraRed) sensor, a ultrasonic
sensor, a videocamera. According to a preferred embodiment of the
present invention, the docking station 12 comprises a laser scanner
as docking sensor. An exemplary laser scanner that may be used on
board the docking station is the UTM-30LX laser scanner by Hokuyo
Automatic Co., LTD
The docking method for charging the mobile robot 11 according to
the present invention will be now described with reference to the
flow chart of FIG. 3.
According to the method of the present invention, when the charge
level of the rechargeable power source of the mobile robot 11
reaches a given threshold, the mobile robot moves towards the
docking station 12 thanks to its autonomous navigation system. In
particular, the navigation system of the mobile robot 11 determines
the position of the mobile robot 11 and computes a route allowing
the robot to approach the docking station 12. These operations are
typically known in the art and hence they will not be described in
greater detail herein after.
Then, according to the present invention, a bidirectional
communication link is set up between the docking station 12 and the
mobile robot 11 allowing the docking station 12 to drive the mobile
robot 11 towards the docking station 12. In order to do this, the
docking station 12 preferably uses the one or more docking sensors
224 allowing getting information about the position of the mobile
robot 11. Moreover, the present invention provides for switching
off most of the mobile robot components during the docking
procedure, except the first module 21, the traction motors and the
circuitry that is necessary to operate them. These operations will
be described in detail herein after.
At step 301 of the method, the mobile robot 11, while approaching
the docking station 12 as driven by its autonomous navigation
system, arrives at the docking region. In particular, the mobile
robot 11 reaches a starting position when its distance D from the
docking station 12 becomes equal to or less than the radius R. The
time at which the mobile robot 11 reaches the starting position
will be referred to in the following description as "starting time"
ts. The distance D of the mobile robot 11 from the docking station
12 at the starting time will be referred to as "starting distance"
and indicated by "Ds". It may be computed as follows Ds= {square
root over (Xs.sup.2+Ys.sup.2)} [1]
where Xs and Ys are, respectively, the X coordinate and the Y
coordinate of the mobile robot 11 within the reference Cartesian
coordinate axes system represented in FIG. 1 at the starting
position. In other words, Xs is the distance of the mobile robot's
starting position from the docking station 12 along the X
(horizontal) axis, and Ys is the distance of the mobile robot's
starting position from the docking station 12 along the Y
(vertical) axis.
When the mobile robot 11 reaches the starting position, the first
control unit 213 preferably generates a status message indicating
that the mobile robot 11 needs charging. The message may be a
message according to a Robot Operating System (ROS), in particular
according to the ROS messaging rules. Then, the first communication
unit 211 preferably sends the status message to the second
communication unit 221 of the docking station (step 302) over the
wireless communication link established between them. In the
meanwhile, the mobile robot 11 preferably stops its one or more
traction motors.
As anticipated above, according to an embodiment of the present
invention, messages exchanged between the docking station 12 and
the mobile robot 11 are carried over wireless signals transmitted
over the direct bidirectional wireless communication link that may
be established between the first communication unit 211 and the
second communication unit 221, using e.g. the Wi-Fi technology.
According to advantageous embodiments, messages are transmitted
between the first communication unit 211 to the second
communication unit 221 over an indirect wireless bidirectional
communication link passing though the cloud platform 23.
At step 304, the second communication unit 221 of the docking
station 12 receives the status message indicating that the mobile
robot 11 needs charging. Upon reception of the status message, the
second control unit 223 preferably generates a command for
switching on the one or more docking sensors 224. At step 305, the
one or more docking sensors 224 preferably switch on and start
emitting the corresponding signal(s). Moreover, at step 306, the
second communication unit 221 preferably generates an
acknowledgment message for the mobile robot 11 indicating that it
received the status message sent by the first communication unit
211 at step 302. It is to be noticed that the second communication
unit 221 may alternatively generate the acknowledgment message
before the docking sensors 224 are switched on. According to other
embodiments of the present invention, the docking sensors 224 may
be already switched on when the mobile robot 11 enters the docking
station (in this case, the flow chart of FIG. 3 does not comprise
step 305).
At step 307, the first communication unit 211 preferably receives
the acknowledgment message from the second communication unit 221
of the docking station 12. Upon reception of the acknowledgment
message, the first control unit 213 preferably generates further
commands for the powerboard of the mobile robot 11 in order to
switch off a number of components of the mobile robot 11. According
to the present invention, most of the components of the mobile
robot 11 are switched off at this point, with the exception of the
components of the first module 21, in particular the first
communication unit 211 and the first control unit 212, the traction
motors and the circuitry that drives the traction motors (step
308). In other words, the commands generated by the first control
unit 213 at step 308 provide for switching off the components of
the mobile robot 11 that are not necessary for the mobile robot 11
to approach the docking station 12 and dock on it, while keeping
switched on the components that are necessary for the docking
procedure, i.e. the components of the first module 21. the traction
motors and the circuitry that drives the traction motors. In
particular, the mobile robot 11 switches off its autonomous
navigation unit comprising the processor and the navigation
sensors.
The procedure of exchanging the status message and the
acknowledgment message may be implemented according to the ROS
messaging rules by invoking a ROS service, which, as known, is a
client-server synchronous mechanism. In this case, the mobile robot
11 acts as a client by invoking the ROS service (which corresponds
to sending the status message) and waits for the answer (which
corresponds to the acknowledgment message) from a server (i.e. the
docking station 12).
At this point, the docking station 12 starts using the docking
sensor(s) 224 to detect the position of the mobile robot 11 within
the docking region and generate corresponding traction commands to
let the mobile robot 11 approach the docking station 12 and connect
to it. The operations performed by the docking station 12 and the
mobile robot 11 are the following: the docking station 12 uses data
received from its docking sensor(s) 224 to compute the distance of
the mobile robot 11; the docking station 12 generates and sends to
the mobile robot 11 a traction command allowing the mobile robot 11
to approach the docking station 12; and the mobile robot 11
receives the traction command and moves accordingly.
This sequence of operations described above is iterated until the
mobile robot 11 docks on the docking station. The procedure
summarized above will be now described in greater detail with
reference to the blocks of FIG. 2 and the flow chart of FIG. 3. It
is to be noticed that iterations involve steps 309-313 of the
flowchart of FIG. 3, as it will be clearer from the following
lines.
At step 309, on the basis of the data received by the docking
sensor(s) 224, the second control unit 223 preferably computes a
distance between the docking station 12 and the mobile robot 11. In
correspondence of a time t is (namely, at the starting time or
after the starting time) the distance D(t) is computed as the
distance between the docking station 12 and the position of the
mobile robot 11, as follows: D(t)= {square root over
(X(y).sup.2+Y(t).sup.2)} [2]
where X(t) and Y(t) are, respectively, the X coordinate and the Y
coordinate of the mobile robot 11 within the reference Cartesian
coordinate axes system represented in FIG. 1 at time t. In
particular, the first data received by the docking sensor(s) 224
after the mobile robot 11 has reached the docking region correspond
to a distance D(ts) substantially equal to the starting distance Ds
of equation [1].
Moreover, at step 309 on the basis of the data received by the
docking sensor(s) 224, the second control unit 223 preferably
computes an orientation .theta. between the docking station 12 and
the mobile robot 11. In correspondence of a time t after the mobile
robot 11 has reached the starting position, the orientation
.theta.(t) is computed, according to an embodiment of the present
invention, as the angle between the Y axis and the straight line
connecting the position of the docking station 12 and the position
of the mobile robot 11 at time t.
At step 310, a check is preferably performed to determine whether
the mobile robot 11 has docked on the docking station 12. The check
is performed by determining whether an electrical connection has
been established between the first electrical contacts of the first
power handling module 212 on board the mobile robot 11 and the
second electrical contacts of the second power handling module 222
on board the docking station 12. When the electrical connection is
established, the second power handling module 222 preferably
communicate with the second control unit 223 to indicate that the
mobile robot 11 has docked on the docking station 12.
In case the check of step 310 is affirmative, the procedure
ends.
If, at step 310, the check is negative indicating that the mobile
robot 11 has not already docked on the docking station, the second
control unit 223, at step 311, preferably computes a translational
speed V(t) for the mobile robot as follows: V(t)=K.sub.V.times.D(t)
[3]
where D(t) is the distance computed at step 306 and K.sub.V is a
speed adjustment coefficient. The speed coefficient K.sub.V may
have a value comprised between 0 and 1, for instance 1. In
particular, the value of the speed adjustment coefficient K.sub.V
may vary as a function of the distance D(t). More in particular,
the speed adjustment coefficient K.sub.V may be, for instance,
directly proportional to the distance D(t) so that it decreases as
the distance D(t) decreases and provide for slowing down the mobile
robot 11 as it approaches the docking station 12.
Moreover, if, at step 310, the check is negative indicating that
the mobile robot 11 has not already docked on the docking station,
the second control unit 223, at step 308, preferably computes a
rotational speed W(t) for the mobile robot as follows:
W(t)=K.sub.W.times..theta.(t) [4] where .theta.(t) is the
orientation computed at step 306 and K.sub.W is an angular
coefficient. The angular coefficient K.sub.W may have a value
comprised between 0 and 1, for instance it may be equal to 1. In
particular, the value of the angular coefficient K.sub.W may vary
as a function of the distance D(t). For instance, it may be
directly proportional to the distance D(t) so that it decreases as
the distance D(t) decreases and provides for driving the mobile
robot 11 to rotate more slowly as it approaches the docking station
12.
Then, at step 311, the computed values of translational speed V(t)
and rotational speed W(t) are preferably used by the second control
unit 223 to generate one or more traction commands for the mobile
robot 11. A traction command is a command suitable for driving the
mobile robot 11 to move according to the computed values of
translational speed and/or rotational speed. A first traction
command may be generated containing the computed translational
speed V(t) and a second traction command may be generated
containing the computed rotational speed W(t). The traction
commands are preferably introduced in a command message that is
subsequently sent by the second communication unit 221 to the first
communication unit 211 on board the mobile robot 11 over the
established communication link. For instance, the command message
may be a message according to the Robot Operating System (ROS)
messaging rules. The docking station 12 may publish the command
message to a topic, for instance the /cmd_vel topic, which is
typically used by a mobile robot to get traction commands. The
command message used for the traction commands may be the Twist
message of the geometry_msgs packet.
At step 312, the command message is received by the first
communication unit 221 on board the mobile robot 11. Then, the
first control unit 221 preferably processes the command message,
extracts the traction commands and uses them to generate control
signals to operate the traction motors of the mobile robot 11 in
accordance with the traction commands (step 313). In this way, the
traction commands are actuated by the traction motors so that the
mobile robot 11 performs a linear translation and/or a rotational
movement allowing it to approach the docking station 12.
While the mobile robot 11 is moving towards the docking station 12,
the docking station 12 preferably iteratively repeats steps 309,
310 and 311. In this way, the docking station 12 monitors the
position of the mobile robot 11 within the docking region and
drives the mobile robot 11 towards the docking station 12. Steps
309-311 are preferably repeated until the mobile robot 11 docks on
the docking station 12. In particular, as described above, Steps
309-311 are preferably repeated until an electrical connection is
established between the first electrical contacts of the first
power handling module 212 on board the mobile robot 11 and the
second electrical contacts of the second power handling module 222
on board the docking station 12.
The present invention provides an "intelligent" system comprising
modules to be installed on board the mobile robot 11 and the
docking station 12, the modules allowing to establish a
bidirectional connection between the mobile robot 11 and the
docking station 12. Hence, the mobile robot 11 may communicate to
the docking station 12 that it has reached the docking region and
the docking station 12 may drive the mobile robot 11 within the
docking region. In order to do so, the docking station 12 emits
docking signals which allow determining the instantaneous position
of the mobile robot 11. Advantageously, the docking signals may be
emitted by the docking station 12 only upon arrival of the mobile
robot 11 in the docking region, thus saving energy. Moreover,
advantageously, the bidirectional connection between the mobile
robot 11 and the docking station 12 may be established through a
cloud computing platform, which may allow providing great
computational resources.
Moreover, the present invention advantageously allows saving energy
on board the mobile robot 11. This is particularly advantageous in
those cases where the level of the on-board battery of the mobile
robot is critically low and it has to approach the docking station
for recharging. Indeed, as described above, thanks to the present
invention, the mobile robot 11 may switch off all its components
(except the first module 21, its traction motors and the circuitry
that drives them) while approaching the docking station 12 within
the docking region and this allows saving a significant amount of
energy. For sake of example, it is assumed that the mobile robot 12
carries a laser scanner as navigation sensor. The laser scanner is
powered by the 12 V on-board battery of the mobile robot 11 and may
consume a current equal to 1 A. Therefore, the power consumed by
the laser scanner is 12 V.times.1 A=12 W. The processor of the
autonomous navigation unit may consume a power equal to 30 W.
Therefore, the mobile robot 11 may consume an overall power at
least equal to 42 W when its autonomous navigation unit is active.
According to the present invention, the power computed here above
may be saved when the mobile robot 11 enters the docking region and
switches off the autonomous navigation unit. Considering a time
interval of about 60 seconds as the time needed for the mobile
robot 11 to dock on the docking station 12 after it enters the
docking region, saving 42 W of electrical power means saving 42
W.times.60 s=2520 J of energy, i.e. 2.5 kJ per minute. In other
words, it means saving 42 W/12 V=3.5 A of supply current from the
on-board battery.
* * * * *